This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
This shield uses a double optical coupler to control an alternating current motor. It is a version of...
In this interesting circuit, a common relay is used as a vibrator to obtain high voltage with a...
This circuit was found in a Popular Electronics of June 1978. The circuit is interleaved between the...